OnlyOS

The operating system

Kernel

• kexit() or call to _exit() syscall ?
• Disable interrupts in exit function

Boot

• Disable fiq, enable irq.
• Check flags values for processor modes in the doc.
• Check flags values for irq and fiq in the doc.
• Stack implementation: FA, FD, EA, ED? Currently ED.
• Init stacks for all modes. Stack sizes in boot.s must match the linker script.
• Clear .bss section.
• Call main function: do not use branch. Address may be out of range.
• Linker script.
• Prefetch abort and data abort modes differences?
• Branch prediction p59 Cortex Guide.

Interrupts/Exceptions handling

• Interruption table.
• Svc call.
• Svc handler
• Abort handler
• Undefined instruction handler
• Irq handler
• Fiq handler: print message.

Value	r0 Code	r1	r2	return (r0)
error	0x00000	Error number	Undefined	0 if success, else 1
UART_putc	0x00100	the char to push	Null	0 if success, else 1
minit	0x00200	process heap_start adress	Null	0 if success, else 1
kmalloc	0x00201	process heap_start adress	Null	adress of memory block

Filesystem driver

• File system (must code diskio.c)

UART driver

• uart_init(): causes crashes
• Mettre uart_strLen dans un fichier util
• Séparer les fichiers du syscalls.c
• Operational mode configuration necesssary?
• uart_write_byte(): is UART_LSR_TX_SR_E necessary?
• uart_write_byte(): alternate version using diferrent register?
• uart_read_byte(): alternate version for signed values?

Misc

How to compile a new source ?

Create a file "makesrc" in the directory of the source(s) file(s) and add the name of the sources inside.
The script will automaticaly reconize the files and compile them.

Bugs for asm source files.

Questions

• fichier tempo en C
• Compilation: use arm instruction (-marm option in gcc)
• Difference .code 32 and .arm: none.

How to compile newlib ?

./configure --target=arm-none-eabi --enable-interwork --enable-multilib --with-gnu-as --with-gnu-ld --disable-shared --disable-libssp --disable-libada --disable-newlib-supplied-syscalls --enable-lite-exit --disable-newlib-multithread

sources : https://gcc.gnu.org/ml/gcc-help/2012-08/msg00190.html ./configure --target=arm-none-eabi --enable-interwork --enable-multilib --with-newlib --disable-nls --disable-shared --disable-threads --with-gnu-ld --with-gnu-as --disable-libssp --disable-libmudflap --disable-libgomp --with-dwarf2 -v --disable-werror --with-cpu=cortex-a8 --with-mode=thumb --enable-target-optspace --with-fpu=fpv4-sp-d16 --with-float=soft --enable-languages=c,c++ --disable-newlib-multithread